Key Engineering Materials Vols. 345-346

Abstract: A novel process for butt welding of thin metal sheets was developed and named as surface friction welding (SFW), which utilizes friction heat and severe plastic deformation like friction stir welding (FSW). The joining mechanism of the SFW is based on not stirring by the pin tool but surface friction between tool shoulder and joining metals. The developed method was successfully applied to butt welding of various metal sheets thinner than 1.5 mm thick. This paper deals with the principle of SFW, the difference between FSW and SFW, the effect of welding parameters, and the microstructure and mechanical properties of welded sheets.

Abstract: For laser-GMA hybrid welds, the relationship between the process parameters and bead shapes was investigated by using the experimental design and the non-linear regression. The weld beads were fitted by two quadratic functions. By the statistical analysis, the primary bead was mainly affected by GMA welding parameters and the root bead was mainly by laser welding parameters. The root bead shaped deeper penetration and shallower width, as the laser power increased for the constant arc power. High laser power resulted in the martensite phase, therefore exhibiting the sudden increase of hardness as approached to the fusion line of the root bead.

Abstract: The welded bracket is an important supporting component with the structural complexity and crucial functional roles in a large-scale agitator. Strength and modal analysis on it are carried out with the finite element analysis software COSMOS/DesignStar according to the equipment’s working behaviours in presence of rational FEA model of the welded bracket being created with 3D CAD software SolidWorks. The conclusion is made from analysis results that the strength criterion is satisfied with operating requirement of the equipment, and the risk area of the tensile stress is explored, moreover, the dangerous natural frequencies are 41Hz and 95Hz which are worked out respectively through modal analysis results. This analysis process is significant for the agitator design. The technique foundation and method are not only set up effectively, but also the utilized data is provided for the product design and successive manufacturing. The lead time of the agitator will be shortened, and the product quality will be improved.

Abstract: As examples of the most typical methods to determine the shear strength of SiC/SiC composite joints, the tensile test of lap joined composite and the asymmetrical four point bending test of butt joined composite were analyzed by using finite element method with the interface element. From the calculation results, it was revealed that the strength in the tensile test was strongly influenced by the residual stress as the increase of the joint layer thickness. In the case of asymmetrical bending test, it was found that the crack initiation point would move due to the residual stress and the strength was also affected by the joint layer thickness.

Abstract: Friction stir welding (FSW) is a solid-state joining process. During FSW, microstructure drastically changes in local region of the workpiece by introduction of frictional heat and severe plastic deformation arising from rotation of the welding tool, which results in inhomogeneous microstructural distribution in the welds. To maintain high reliability of the structure produced by FSW, precise understanding of microstructural factors governing weld properties is required. In the present paper, microstructural factors governing mechanical properties, especially hardness profile and tensile properties, of friction stir welded Al and Mg alloys are reviewed.

Abstract: Copper/aluminum/stainless steel (Cu/Al/STS) clad materials were made by rolling and heat treatment process. These specimens were evaluated the formability and bonding strength of Cu/Al/STS clad materials. Thin disc specimens for TEM observation were prepared from the interfaces of Cu/Al and Al/STS by using the Focused Ion Beam (FIB) utility. Brittle oxide film formed on copper surface during heat treatment at 673K~773K. Diffusion bonding was observed at the interface of Cu/Al. Reacted region was formed in the interface of Al/STS with width about 10nm, while in the case of Cu/Al was formed about 1,600nm width. It was also observed nanosized crevice in reacted region of Al/STS interfaces.

Abstract: Composites have become the chosen material for new engineering materials specially in the areas of aerospace applications, military weapon and automotive components, due to its unique mechanical properties, like: high strength weigh ratio, extreme thermal shock resistance, low coefficient of thermal expansion, oxidation and wear resistance Polyester resin matrix composites reinforced with coconut fibers are being utilized as replacement synthetic fiber in fiberglass products. The high price of synthetic fiber, which is use as fiber reinforcement on fiberglass products, makes its products price become expensive. One alternative to reduce its prices is by replace fiber synthetic with other fiber, which have similar mechanical properties but cheaper and still not abandon regional potency. Coconut fiber are regional potency that still not used optimally, moreover they often considered as waste that doesn’t have economic values. These research use experimental methods with control variables are percentage of coconut fiber and polyester resin by Planar and Random orientation fiber. Specimen testing makes by hand lay up fabrication. The research result shows that the optimum composition is on 40% fiber: 60% polyester resin, with value of tensile strength is 20.75 N/mm2 and value of strain is 0,7 % by planar orientation fibers, while optimum composition on random orientation is on 30% fiber: 70% polyester resin, with value of tensile strength is 30.73 N/mm2 and value of strain is 1.4%.

Abstract: Mechanical properties of nano/micro-silica particles bidispersed epoxy composites were investigated based on experimental results. The composite specimens varied with different compositions of nano and micro-silica particles (240 nm and 1.56$m) were prepared with the constant volume fraction, 0.30. The thermo-viscoelastic properties for the composites and the neat epoxy measured in the temperature ranges from 123 K to 523 K and compared to theoretical results according to Lewis and Nielsen’s law with the maximum particle packing given by Ouchiyama and Tanaka’s model. In addition, fragility derived from the thermo-viscoelasticity measurements was used to characterize the strength and fracture toughness of the composites. From results, we found that the thermo-viscoelasticity of the composite was dependent on nano and micro-particles packing, and its strength and fracture toughness were effectively evaluated by fragility.

Abstract: The effect of adding a high molecular weight epoxy monomer (epikote 1001) to a low molecular weight one (epikote 828) on fracture toughness properties was investigated according to the crosslinking degree and density heterogeneity. To characterize the crosslinking degree and density heterogeneity, the glass transition temperature, Tg, and fragility, m, were deduced from thermo-viscoelastic properties. The characterization of Tg and m revealed that blends can be divided into two groups: one group with (φ < 10 wt%) and another one with (φ > 10 wt%), where φ is the weight ratio of epikote 1001 to epikote 828. The first group had the same average crosslinking degree (the same Tg) but different density heterogeneities (m decreased). The other group had a lower crosslinking degree (Tg decreased) and even more density heterogeneity (m decreased). The fracture toughness results showed that KIC of blends of the first group was approximately constant because the increase in density heterogeneity was still too weak (ineffective m), whereas KIC of blends of the second group was higher due to the simultaneous decrease in average crosslinking degree and increase in density heterogeneity. Therefore, the lower crosslinking degree (lower Tg) is and the more heterogeneous the blend (lower m) is due to the addition of high molecular weight monomer, the higher KIC becomes.

Abstract: Two different processes were used to manufacture epoxy/silica hybrid materials. Observations by AFM, TEM, and Raman spectroscopy demonstrated different silica structures, depending on the hybrid process. DMTA results indicated that the “sequentially” hybridised sample had a new glass transition at higher temperatures, which could be attributed to the physical interaction between the silica chain and the epoxy resin. The dynamic modulus was significantly improved and depended only on the silica content, not on the silica structure nor the aging.